diff options
Diffstat (limited to 'gdb/i386-linux-nat.c')
| -rw-r--r-- | gdb/i386-linux-nat.c | 246 |
1 files changed, 246 insertions, 0 deletions
diff --git a/gdb/i386-linux-nat.c b/gdb/i386-linux-nat.c index 3239801..ca87ffd 100644 --- a/gdb/i386-linux-nat.c +++ b/gdb/i386-linux-nat.c @@ -1042,6 +1042,252 @@ i386_linux_skip_solib_resolver (CORE_ADDR pc) } +/* Recognizing signal handler frames. */ + +/* Linux has two flavors of signals. Normal signal handlers, and + "realtime" (RT) signals. The RT signals can provide additional + information to the signal handler if the SA_SIGINFO flag is set + when establishing a signal handler using `sigaction'. It is not + unlikely that future versions of Linux will support SA_SIGINFO for + normal signals too. */ + +/* When the i386 Linux kernel calls a signal handler and the + SA_RESTORER flag isn't set, the return address points to a bit of + code on the stack. This function returns whether the PC appears to + be within this bit of code. + + The instruction sequence for normal signals is + pop %eax + mov $0x77,%eax + int $0x80 + or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80. + + Checking for the code sequence should be somewhat reliable, because + the effect is to call the system call sigreturn. This is unlikely + to occur anywhere other than a signal trampoline. + + It kind of sucks that we have to read memory from the process in + order to identify a signal trampoline, but there doesn't seem to be + any other way. The IN_SIGTRAMP macro in tm-linux.h arranges to + only call us if no function name could be identified, which should + be the case since the code is on the stack. + + Detection of signal trampolines for handlers that set the + SA_RESTORER flag is in general not possible. Unfortunately this is + what the GNU C Library has been doing for quite some time now. + However, as of version 2.1.2, the GNU C Library uses signal + trampolines (named __restore and __restore_rt) that are identical + to the ones used by the kernel. Therefore, these trampolines are + supported too. */ + +#define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */ +#define LINUX_SIGTRAMP_OFFSET0 (0) +#define LINUX_SIGTRAMP_INSN1 (0xb8) /* mov $NNNN,%eax */ +#define LINUX_SIGTRAMP_OFFSET1 (1) +#define LINUX_SIGTRAMP_INSN2 (0xcd) /* int */ +#define LINUX_SIGTRAMP_OFFSET2 (6) + +static const unsigned char linux_sigtramp_code[] = +{ + LINUX_SIGTRAMP_INSN0, /* pop %eax */ + LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */ + LINUX_SIGTRAMP_INSN2, 0x80 /* int $0x80 */ +}; + +#define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code) + +/* If PC is in a sigtramp routine, return the address of the start of + the routine. Otherwise, return 0. */ + +static CORE_ADDR +i386_linux_sigtramp_start (CORE_ADDR pc) +{ + unsigned char buf[LINUX_SIGTRAMP_LEN]; + + /* We only recognize a signal trampoline if PC is at the start of + one of the three instructions. We optimize for finding the PC at + the start, as will be the case when the trampoline is not the + first frame on the stack. We assume that in the case where the + PC is not at the start of the instruction sequence, there will be + a few trailing readable bytes on the stack. */ + + if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) + return 0; + + if (buf[0] != LINUX_SIGTRAMP_INSN0) + { + int adjust; + + switch (buf[0]) + { + case LINUX_SIGTRAMP_INSN1: + adjust = LINUX_SIGTRAMP_OFFSET1; + break; + case LINUX_SIGTRAMP_INSN2: + adjust = LINUX_SIGTRAMP_OFFSET2; + break; + default: + return 0; + } + + pc -= adjust; + + if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) + return 0; + } + + if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0) + return 0; + + return pc; +} + +/* This function does the same for RT signals. Here the instruction + sequence is + mov $0xad,%eax + int $0x80 + or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80. + + The effect is to call the system call rt_sigreturn. */ + +#define LINUX_RT_SIGTRAMP_INSN0 (0xb8) /* mov $NNNN,%eax */ +#define LINUX_RT_SIGTRAMP_OFFSET0 (0) +#define LINUX_RT_SIGTRAMP_INSN1 (0xcd) /* int */ +#define LINUX_RT_SIGTRAMP_OFFSET1 (5) + +static const unsigned char linux_rt_sigtramp_code[] = +{ + LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */ + LINUX_RT_SIGTRAMP_INSN1, 0x80 /* int $0x80 */ +}; + +#define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code) + +/* If PC is in a RT sigtramp routine, return the address of the start + of the routine. Otherwise, return 0. */ + +static CORE_ADDR +i386_linux_rt_sigtramp_start (CORE_ADDR pc) +{ + unsigned char buf[LINUX_RT_SIGTRAMP_LEN]; + + /* We only recognize a signal trampoline if PC is at the start of + one of the two instructions. We optimize for finding the PC at + the start, as will be the case when the trampoline is not the + first frame on the stack. We assume that in the case where the + PC is not at the start of the instruction sequence, there will be + a few trailing readable bytes on the stack. */ + + if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) + return 0; + + if (buf[0] != LINUX_RT_SIGTRAMP_INSN0) + { + if (buf[0] != LINUX_RT_SIGTRAMP_INSN1) + return 0; + + pc -= LINUX_RT_SIGTRAMP_OFFSET1; + + if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) + return 0; + } + + if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0) + return 0; + + return pc; +} + +/* Return whether PC is in a Linux sigtramp routine. */ + +int +i386_linux_in_sigtramp (CORE_ADDR pc, char *name) +{ + if (name) + return STREQ ("__restore", name) || STREQ ("__restore_rt", name); + + return (i386_linux_sigtramp_start (pc) != 0 + || i386_linux_rt_sigtramp_start (pc) != 0); +} + +/* Assuming FRAME is for a Linux sigtramp routine, return the address + of the associated sigcontext structure. */ + +CORE_ADDR +i386_linux_sigcontext_addr (struct frame_info *frame) +{ + CORE_ADDR pc; + + pc = i386_linux_sigtramp_start (frame->pc); + if (pc) + { + CORE_ADDR sp; + + if (frame->next) + /* If this isn't the top frame, the next frame must be for the + signal handler itself. The sigcontext structure lives on + the stack, right after the signum argument. */ + return frame->next->frame + 12; + + /* This is the top frame. We'll have to find the address of the + sigcontext structure by looking at the stack pointer. Keep + in mind that the first instruction of the sigtramp code is + "pop %eax". If the PC is at this instruction, adjust the + returned value accordingly. */ + sp = read_register (SP_REGNUM); + if (pc == frame->pc) + return sp + 4; + return sp; + } + + pc = i386_linux_rt_sigtramp_start (frame->pc); + if (pc) + { + if (frame->next) + /* If this isn't the top frame, the next frame must be for the + signal handler itself. The sigcontext structure is part of + the user context. A pointer to the user context is passed + as the third argument to the signal handler. */ + return read_memory_integer (frame->next->frame + 16, 4) + 20; + + /* This is the top frame. Again, use the stack pointer to find + the address of the sigcontext structure. */ + return read_memory_integer (read_register (SP_REGNUM) + 8, 4) + 20; + } + + error ("Couldn't recognize signal trampoline."); + return 0; +} + +/* Offset to saved PC in sigcontext, from <asm/sigcontext.h>. */ +#define LINUX_SIGCONTEXT_PC_OFFSET (56) + +/* Assuming FRAME is for a Linux sigtramp routine, return the saved + program counter. */ + +CORE_ADDR +i386_linux_sigtramp_saved_pc (struct frame_info *frame) +{ + CORE_ADDR addr; + addr = i386_linux_sigcontext_addr (frame); + return read_memory_integer (addr + LINUX_SIGCONTEXT_PC_OFFSET, 4); +} + +/* Offset to saved SP in sigcontext, from <asm/sigcontext.h>. */ +#define LINUX_SIGCONTEXT_SP_OFFSET (28) + +/* Assuming FRAME is for a Linux sigtramp routine, return the saved + stack pointer. */ + +CORE_ADDR +i386_linux_sigtramp_saved_sp (struct frame_info *frame) +{ + CORE_ADDR addr; + addr = i386_linux_sigcontext_addr (frame); + return read_memory_integer (addr + LINUX_SIGCONTEXT_SP_OFFSET, 4); +} + + /* Register that we are able to handle Linux ELF core file formats. */ static struct core_fns linux_elf_core_fns = |